Litter production and decomposition in the New Zealand mangrove,Avicennia marinavar.resinifera

Abstract

The New Zealand mangrove, A. marina var. resinifera, grows close to the latitudinal limit of mangroves. Nevertheless, litterfall studies in Tuff Crater, Auckland (36.degree. 48'' S, 174.degree. 45'' E), using litter-fall bag and plot techniques, indicate that the mangroves are very productive. Litter fall beneath 2 distinct growth forms of the mangrove is seasonal, with peak fall at the time of fruit production in summer. Beneath the taller mangroves of the creek banks (3.5-4.0 m tall) annual total dry weight of litter fall is estimated as 8.10 .+-. 2.74 t [tons] ha-1 a-1, whereas beneath the lower, stunted mangroves of the flats (< 1.0 m tall), the total is estimated as 3.65 t ha-1 a-1. The values from the taller mangroves are higher than litter fall recorded beneath Avicennia at similar latitudes in Australia, and lie within the range reported from mangroves in Queensland, Florida [USA], and elsewhere. In terms of litter, mangroves may be one of the most productive forest types in New Zealand. The rate of decomposition of mangrove leaves, using the litter bag technique, was rapid, with half of the ash-free weight being lost in 6-8 wk. Differences between decomposition rates in summer and in winter appeared small, and site-specific differences were not discernible.